WO2006108759A1

WO2006108759A1 - Method for voltametric electrochemical analysis and implementing device therefor

Info

Publication number: WO2006108759A1
Application number: PCT/EP2006/061112
Authority: WO
Inventors: Olivier Lavastre; Didier Floner; Florence Geneste
Original assignee: Universite De Rennes 1
Priority date: 2005-04-12
Filing date: 2006-03-28
Publication date: 2006-10-19
Also published as: US20080190782A1; EP1869439A1; CN101184992A; FR2884318B1; CA2608080A1; FR2884318A1

Abstract

The invention concerns a method for voltametric electrochemical analysis of a liquid solution, for detecting and/or assaying in said solution at least one chemical species. The invention is characterized in that the method includes the following steps: contacting a sample of said solution with a single analyzing support (10) having at least two working electrodes (12) each belonging to a separate electrochemical analysis cell, each analysis cell further including a counter-electrode (13) and a reference electrode; performing a single and different measurement of said sample in each of said analysis cells, by applying an independent and different potential to each of the working electrodes (12); producing at least one voltamogram of said sample, based on said measurements; deducing from said voltamogram data concerning the detection and/or assay of said at least one chemical species in said sample.

Description

ELECTROCHEMICAL VOLTAMETRIC ANALYSIS METHOD AND DEVICE FOR IMPLEMENTING THE SAME

The field of the invention is that of chemistry and more specifically methods for electrochemical analysis of liquid solutions or gases for the detection and / or assay of chemical species.

A technique for qualitative and quantitative analysis of electrochemical species commonly used is voltammetry. This technique is based on the measurement of the current flow resulting from the reduction or oxidation of the species present under the effect of a controlled variation of the potential difference between two electrodes.

A large number of species (or compounds) can thus be analyzed, whether organic or inorganic compounds, cations or anions.

A voltammetric analyzer is thus composed of an electrochemical analysis cell based on a three-electrode system immersed in the solution to be analyzed.

The three electrodes are:

a working electrode (also called indicator electrode);

a reference electrode; and - a counter-electrode (also called auxiliary electrode).

The voltammetric analyzer is also composed of a potentiostat making it possible to impose a potential difference between the working electrode and the counter-electrode, and to impose a specific and constant potential on the reference electrode so that the potential imposed on the working electrode is precisely defined.

The curves I = f (E) obtained represent the current measured (at precise times during the imposition of the potential) as a function of the potential, and make it possible to determine qualitatively and / or quantitatively the chemical species or species present in the solution. These curves allow such access to the value of the diffusion limit current Iumi _you, proportional to the concentration of the species, and value of the half-wave potential Ey ₂ (also called half-reaction potential) characteristic of the oxidized or reduced species.

The current i can be measured continuously and the curve I = f (E) obtained is called the voltammogram. Different voltametric analysis techniques can be implemented depending on the variation of the imposed potential, which can be linear or modulated.

A first known technique is the step scan voltammetry, also called potential jump voltammetry (SCV: Staircase Voltammetry). According to this technique, a series of regularly increasing value (constant jump height) and constant duration (staircase step) steps is applied, and the current is measured by sampling after a certain duration of the step. When the duration and the height of the bearing are sufficiently weak, the method is equivalent to linear potential scanning voltammetry (LSV: Linear Scan Voltammetry). A second known technique is potential voltammetry also called normal impulse voltammetry (NPV: Normal Puise Voltammetry). According to this technique, a series of potential pulses is imposed and the intensity of the current is measured after a certain time "t" after the jump. After each pulse, the potential returns to its initial value and the height of each pulse is varied regularly so as to carry out a scanning potential exploration.

A third known technique is differential voltage voltammetry, also known as Differential Pulse Voltammetry (DPV). According to this technique, a series of potential pulses is imposed and the current difference before and after the jump is measured. Each impulse is of constant height, but the return potential is different from the potential before impulse, which allows a potential evolution and a potential exploration. Each measured current difference is plotted as a function of the potential reached by the jump, which amounts to representing the derivative of the curve I = f (E) when the interval between two measurements tends to zero. Moreover, electrochemical analysis methods use different types of electrodes, and in particular, different types of working electrodes.

According to the simplest method, a solid working electrode is immersed in the solution to be analyzed. It may be of different natures, that is to say made in different conductive materials, such as

- metals (Platinum, Gold, Silver, Copper or Nickel for example, or alloys);

non-metallic materials (graphite or vitreous carbon, for example);

organic materials such as polymers for example. The working electrode used for the analysis can then be chosen in particular according to the oxidation or reduction potential of a particular species that it is desired to analyze. However, this method has two major disadvantages. First, during measurements, adsorption phenomena, deposition, or even corrosion of the electrode are likely to occur and modify the surface of the electrode by disturbing the current response.

On the other hand, it is also necessary to take into account the variation of the concentration of the substrate (or chemical species) studied with the variation of the potential. Indeed, during the electrolysis of the oxidant for example, the concentration of the substrate on the surface of the electrode decreases with respect to its initial concentration in the solution, far from the electrode. This phenomenon is at the origin of a concentration gradient and the appearance of a diffusion layer whose thickness is generally a few microns on the surface of the electrode.

The following formula describes the relationship between the intensity of the current I and the concentration C _0x of the substrate (i.e., the oxidant):

T _ (f-Λ solution (-Λ electrode)

1 - Hi ₀ (Cox - Co _x ), in which Hi ₀ is the material transport coefficient of the oxidant. In order to overcome these drawbacks, techniques known from the prior art provide for various alternatives such as stirring the solution during the measurements by a magnetic stirrer for example, or the use of a rotating electrode. The rotating electrode consists of a disk-forming electrode, which can for example be made of platinum, silver or vitreous carbon, and driven by a rotational movement.

If these techniques actually make it possible to homogenize the solution and therefore to renew it at the electrode, on the other hand, they do not allow the renewal of the surface of the electrode during the measurements, which is then subjected to risks of alteration described above.

The known method for renewing the active surface of the disk electrode is the mechanical polishing thereof. Therefore, the establishment of the curve I = f (E) must be done point by point, with the obligation to implement the polishing of the electrode between each measurement. In addition, the intensity of the current must be measured at a precise time after the imposition of the potential. It is easy to understand that the establishment of this curve is tedious, very long, and includes many erroneous points.

Another known technique of the prior art makes it possible to ensure the renewal of the surface of the working electrode with each measurement. This is the mercury drop electrode. According to this technique called polarography, a drop of mercury grows at the end of a capillary fed with mercury continuously. The size of the drop increases until it breaks off under the effect of its weight. A new drop is then formed at the end of the capillary. The drop is thus renewed at each measurement and is substantially identical to the previous one. The current is measured at a specific time during the lifetime of the drop or is a value averaged over the entire life of the drop.

Thus, this technique effectively ensures the renewal of the active surface of the electrode. Moreover, the drop of the drop ensures the agitation of the solution and cancels out the effect of depletion in the substrate. So, each new drop begins its growth in a solution corresponding to the initial solution.

However, a first disadvantage of this technique is that it requires the use and handling of mercury which is a toxic compound and which therefore requires special and restrictive conditions of use to meet the current standards of hygiene, safety and security. environmental.

Another disadvantage of this technique is that the mercury electroactivity range is between +0.2 V and -2 V, depending on the pH of the solution. This field allows a study of electroactive species up to a cathodic value not reached by other metals. On the other hand, this area is very limited on the anodic side (+0.2 V), unlike other materials (for example +1.5 V for platinum and gold, +1.8 V for carbon, etc.) The invention particularly aims to overcome these disadvantages of the prior art.

More specifically, an object of the invention is to provide a new technique for a simple and rapid analysis of a solution, and in particular the detection and / or rapid assay of one (or more) chemical species.

Another objective of the invention is to propose a powerful technique making it possible to overcome the phenomenon of depletion in species of the solution which has reacted in the vicinity of the working electrode, as well as to avoid surface alteration. activates the working electrode during measurements, so that the measurements made are rigorous and precise.

Yet another particular object of the invention, to which certain embodiments respond, is to propose a technique offering a good modularity as to the oxidation-reduction potential of the species to be analyzed and which is simple to implement by the method. 'user. These objectives, as well as others, which will become clearer later, are achieved by an electrochemical analysis method. voltammetry of a liquid solution, allowing detection and / or dosage in said solution of at least one chemical species.

According to the invention, the method comprises the steps of:

contacting a sample of said solution with a single analysis support having at least two working electrodes each belonging to a separate electrochemical analysis cell, each analysis cell further comprising a counter-electrode and a test electrode; reference;

performing a single and different measurement of said sample in each of said analysis cells, by applying an independent potential to each of said working electrodes; establishing at least one voltammogram of said sample from said measurements;

deducing from said voltammogram information relating to the detection and / or the assay of said at least one chemical species in said sample.

Thus, the invention consists in analyzing a solution by means of a single analysis support having a plurality of working electrodes, each of them being used only for the realization of a single measurement, independent potentials being applied.

According to this technique, insofar as each working electrode is only used for a single measurement, these are therefore renewed for each of the measurements.

An analysis cell for performing a measurement comprises:

- a working electrode

a counter-electrode; and

a reference electrode.

As indicated above, the working electrode of each analysis cell is located on the analysis support. On the other hand, as will be explained later, the counter-electrode and / or the reference electrode completing an analysis cell can, for their part, be located on the same analysis medium or, on the contrary, be carried on a second support

(also called complementary support) separate from the analysis support for example. The notion of "distinct" analysis cell means that the working electrodes of the different cells are distinct. However, as will be explained later, a counter-electrode and / or a reference electrode may, on the other hand, be common to several or all the analysis cells. The chemical species present in the solution and analyzed by this process can be ionic, molecular or gaseous (in the form of a dissolved gas).

Advantageously, the same sample of the solution is in contact

(simultaneously) with all the electrochemical cells of the analysis support during the measurements (that is to say with all the electrodes constituting an analysis cell). The analysis support may for example be immersed in the sample of the test solution.

According to a first advantageous embodiment of the invention, the measurements are carried out simultaneously by each of the analysis cells. The independent potentials are then applied simultaneously to the working electrodes of the different cells.

Each measurement being performed at the same time, the composition of the sample is identical at the level of each electrode and corresponds to the initial composition. In addition, this makes it possible to reduce as much as possible the time required for the establishment of the voltammogram (s) and therefore for the analysis of the sample.

According to a second advantageous embodiment of the invention, the measurements are carried out successively by the analysis cells. Advantageously, the duration separating two successive measurements will be less than a maximum duration. Limitation of the delay between two measurements ensures that the current response in a cell is not impaired by electrochemical reactions taking place in neighboring cells. At the moment when a measurement is made, the composition of the sample in the vicinity of the cell is not modified by the previous measurement or measurements and is therefore not depleted in the chemical species reacted during the measurement.

In addition, the limitation of the duration between the measurements by the different analysis cells also makes it possible to reduce the overall time required for the analysis of the sample.

Advantageously, when the measurements are carried out successively by the different cells, a counter-electrode and / or a reference electrode are common to at least two analysis cells. Indeed, it will then be possible to provide that a same counter-electrode and / or the same reference electrode is used for making measurements by different cells, the measurements being carried out successively, and these electrodes not risking to not alter during measurements.

The reference electrode and / or the counter-electrode common to different analysis cells may be located on the analysis support carrying the working electrodes, or on a complementary support.

Moreover, it will of course be possible to combine the two preceding modes by considering that the measurements are carried out at the same time for certain electrochemical cells, and that, on the other hand, they are slightly shifted in time for certain other cells of analysis.

It is thus understood that the technique of the invention allows rapid analysis of a sample insofar as the different measurements can be performed simultaneously. One or more different voltammograms can thus be established and exploited from the measurements made.

Advantageously, said measurements made allow the implementation of at least one voltametric analysis belonging to the group comprising: voltammetry by potential jump; normal impulse voltammetry; differential pulse voltammetry.

These different analysis methods can also be combined for the same analysis medium, a first set of cells that can allow the establishment of a voltammetry voltammet by jump potential and a second set of cells that can establish a voltammogram by differential pulse voltammetry for example to increase the sensitivity of the analysis.

The combination of the different types of analysis will thus make it possible to obtain more precise results as regards the determination of the species present and their concentration.

Advantageously, the method according to the invention can be implemented prior to further study and more accurate sample. It will thus be possible to use a support having a reduced number of working electrodes for the establishment of a voltammogram, so as to rapidly determine the presence or absence of a particular chemical species in the solution for example.

For example, at least ten measurements can be used from ten working electrodes to establish a voltammogram. The greater the number of measurements taken to establish a voltammogram, the more precise the analysis will be.

The invention also relates to an analysis support for the implementation of an electrochemical analysis method as described above. Such a support has at least two working electrodes each belonging to a separate electrochemical analysis cell, and it furthermore has at least one electrical connection network allowing application of an independent potential to each of the working electrodes.

Thus, several working electrodes are distributed on an analysis support and each allow the realization of a single and independent measurement, the network of electrical connections for applying an independent potential to different working electrodes. An analysis support according to the invention may also be called "analysis plate" or "plate" or "chip".

Advantageously, the different working electrodes of an analysis support are of the same dimensions. In particular, the working electrodes belonging to the cells used for the establishment of the same voltammogram are of the same dimensions. It is indeed important during the measurements that the working electrodes making it possible to carry out measurements making it possible to establish a voltammogram have a substantially identical active surface. Preferably, at least two of the analysis cells comprise a working electrode made of different materials. It may indeed be provided that the working electrodes of the same analysis medium (or chip) are made with different materials.

This may make it possible to establish several voltammograms from the same analysis medium, each voltammogram corresponding to the measurements obtained from cells whose working electrodes are of the same natures.

When detecting and / or analyzing a chemical species, all the working electrodes are not necessarily adapted, in particular as a function of the material in which the working electrode and the oxidation-reduction potential of the electrode are produced. the species to be analyzed, or the pH conditions of the solution.

Thus, it may be necessary to consider different types of working electrode for the analysis of the chemical species of a solution. It is therefore understandable that the use of a support having working electrodes of different natures.

Advantageously, said working electrodes of the analysis cells are made of at least one material belonging to the group comprising metals and non-conducting metals.

The metals used may for example be gold, platinum, silver, copper, chromium, zinc, tin, nickel or lead or alloys. Non-metallic and conductive materials may for example be the graphite, vitreous carbon, doped silicon or organic materials such as conductive polymers (polypyrrole, polythiophene or polyanaline for example).

The working electrodes may also be chemically modified electrodes. Such modified electrodes thus have a mediator for reacting in the presence of one or more particular chemical species of a solution to be analyzed. The mediator can be covalently attached to the working electrode or by adsorption phenomena.

The use of a modified electrode may in particular allow the detection and / or the determination of non-electroactive substances.

The modification of the surface of the electrode can be done by immobilization for example of organic compounds, organometallic or ionic fragments, strands of DNA, enzymes or other molecules of high molecular weight. In addition, voltammetric analysis can be difficult in the case of solutions comprising several different chemical species. In fact, a measurement by an analysis cell may then be due to several compounds and not be characteristic of a single chemical species.

The use of a support having working electrodes of different natures may thus allow a discriminant analysis of the different species by comparison of the different voltammograms obtained with each of the different electrodes. Indeed, the behavior of the chemical species is variable depending on the working electrode used.

Different voltammograms will then be established from measurements made by analysis cells whose working electrodes are of different natures.

In a preferred manner, the working electrodes used for producing the same voltammogram are of the same dimensions.

Preferably, the working electrodes of the different analysis cells are distributed on the same face of the analysis support. The sample of the solution to be analyzed may for example be deposited on this side of the analysis support.

Advantageously, the working electrodes are at least 100 μm apart. Advantageously, the method according to the invention can be implemented prior to further study and more accurate sample. Thus, a reduced number of measurements (and therefore a reduced number of working electrodes) can be used to establish a voltammogram so as to rapidly determine the presence or absence of a particular chemical species in the solution. example.

By way of example, it will be possible to use an analysis support having one hundred working electrodes. These may for example be divided into ten lines of ten. In general, the higher the number of measurements taken to establish a voltammogram, the more precise the analysis will be. Moreover, the larger the number of working electrodes of different natures is used, the more precise the analysis will be in that it will allow analysis of very different chemical species of oxidation-reduction potentials.

In addition, this will allow a better interpretation of the voltamograms obtained. The comparison of the voltammograms established from measurements obtained by working electrodes of different types makes it possible to determine whether the curves obtained are characteristic of a single species or, on the contrary, of several different chemical species.

For example, in the case of an analysis support having one hundred working electrodes, it is possible to provide a distribution of the latter over ten lines, with working electrodes of different natures located on different lines.

Advantageously, the working electrodes of the different cells are of the same shapes and dimensions and therefore have a substantially identical active surface.

As indicated previously, an analysis cell is composed of: - a working electrode;

a counter-electrode; and

- a reference electrode.

According to a first advantageous approach of the invention, provision may be made for the counter-electrodes and / or the reference electrodes completing an analysis cell are also located on the analysis support carrying the working electrodes. In this case, they will preferably be located near the working electrode of the analysis cell to which they belong. According to this approach of the invention, it can be provided that, according to a first embodiment, each counter-electrode and each reference electrode are specific to an analysis cell. In particular, when the measurements are carried out simultaneously by each of the analysis cells, the potentials being applied simultaneously to the different working electrodes. When the different electrodes composing an analysis cell are specific to it and located close to each other, they can be grouped together on an area measuring 100 μm to 1000 μm for example, each of the zones then defining a cell. analysis, and the different zones can be separated by a distance of 10 microns to 1 mm. However, it may also be provided, according to a second embodiment, a counter electrode and / or a reference electrode is common to several analysis cells.

This may in particular be the case when the measurements are carried out successively, that is to say, when the potentials are successively applied to the different working electrodes.

It may also be provided according to this embodiment that the analysis support carrying the working electrodes also comprises a counter-electrode in the vicinity of each working electrode, and that the counter-electrodes are electrically connected to each other. This makes it possible for each working electrode to be spatially close to the common counter electrode. The use of common counter-electrodes and / or of common reference electrodes during measurements carried out successively in particular makes it possible to limit the number of electrical connections on the analysis support. This simplifies and limits the costs of manufacturing them.

The invention also relates to a complementary support, intended to cooperate with an analysis support as presented, having at least one counter-electrode and / or at least one reference electrode belonging to the analysis cells. Indeed, according to a second advantageous approach of the invention, it can be provided that the counter-electrodes and / or the reference electrodes completing an analysis cell are located on a complementary support, and not on the analysis support bearing the working electrodes.

They will then be preferentially distributed so that the three electrodes forming an analysis cell, and allowing the realization of a measurement, are close to each other. The complementary support may for example be placed facing the analysis support, parallel to it, a small distance separating them.

The distance separating the two supports may for example be 5 mm.

The counter electrodes and / or the reference electrodes may then be placed on the complementary support so that they are directly opposite the working electrode with which they form an analysis cell. The space between the two supports will then preferably comprise the sample of the solution to be analyzed so that it is in contact simultaneously with the two supports (that is to say with the different electrodes carried by the supports) .

We can of course also combine the two approaches and provide that the counter electrodes are located on the analysis support, close to each working electrode, and that only the reference electrodes are located on the complementary support, or vice versa.

As in the previous case, two embodiments can be envisaged according to this second approach: According to a first embodiment, each reference electrode and each counter-electrode is specific to each analysis cell. This will be the case, especially when measurements are performed simultaneously by each analysis cell.

According to a second embodiment of the invention, it will be possible to provide on the contrary a single counter-electrode and / or a single reference electrode common to the different cells of analysis, as described above. This may in particular be the case when the measurements are carried out successively, that is to say when the potentials are successively applied to the different working electrodes. A single reference electrode and / or a single counter electrode located on the complementary support can then be common to the different working electrodes.

The complementary support carrying the common counter electrode and / or the common reference electrode may for example be in the form of a ribbon. It is indeed advantageous for the accuracy of the measurements that the reference electrode and / or the counter-electrode are common to the different working electrodes of the analysis support.

The use of common counter-electrodes and / or of common reference electrodes during measurements carried out successively in particular makes it possible to limit the number of electrical connections for the complementary support carrying them and thus makes it possible to simplify and limit the costs associated with to its manufacture.

Moreover, when, according to the second approach of the invention, a complementary support carrying the counter-electrode or electrodes and / or the reference electrode or electrodes is used, it may then be reused for later analyzes, after have been properly washed. Indeed, the one or more counter-electrodes and / or the reference electrode or electrodes have no risk of tampering when used, unlike working electrodes. Thus, successive measurements using the same complementary support does not therefore risk to alter the accuracy of the measurements.

This makes it possible to limit the costs by not systematically changing at each analysis that the analysis support carrying the working electrodes.

The invention also relates to a device for implementing an electrochemical analysis method as described above. Such a device comprises: first means for receiving at least one analysis medium as described above, second means for receiving at least one sample; means for contacting said at least one analysis support and said sample; means for applying an independent potential to each of said working and measuring electrodes of said sample in each of said analysis cells.

The device thus comprises receiving means at which the analysis support is placed for each analysis. Each support being used for only one analysis. It may also be provided that the device is designed to receive several analysis media, iççon to simultaneously perform the analysis of different samples may come from different solutions.

Preferably, the device comprises means for establishing at least one voltammogram from the measurements. Furthermore, the device may also comprise third means for receiving a complementary support as described above, comprising at least one counter-electrode and / or at least one reference electrode, as well as means for contacting said sample. and said complementary support. This case will be considered when the analysis support carrying the working electrodes of the analysis cells does not bear, on the other hand, the electrodes of reference and / or counter electrodes. It has already been indicated previously that one and / or the other of these may be located on a complementary support.

Advantageously, the device also comprises means for deducing from said at least one voltammogram information relating to the detection and / or the assay of said at least one chemical species in the sample.

Such a device thus makes it possible to quickly establish one or more voltammograms and the analysis of the species present in a sample of a solution.

Advantageously, the device is portable (or portable). It is of course understood that it is advantageous to enable the production of a portable device in relation to the methods known in the prior art and allowing a rigorous voltammetric analysis, such as polarography using a mercury drop electrode, which implement a equipment voluminous and expensive, and therefore difficult to move.

The device according to the invention can thus be transported and used directly where the solution to be analyzed is located, in order to determine, for example, whether further analysis is necessary and then to carry it out in the laboratory.

Other characteristics and advantages of the invention will emerge more clearly on reading the following description of a preferred embodiment of the invention, given by way of illustrative and nonlimiting example, and the appended drawings among which: FIG. 1 shows a voltammogram obtained by a technique known from the prior art for a solution of Fe ³⁺ at a concentration of 10 ^-2 mol / ^l in sulfuric acid H ₂ SO ₄ at 0.5 moLL ^"1 ; FIGS. 2A, 2B and 2C are simplified and schematic views of an analysis support according to the invention; FIGS. 3A and 3B respectively show the current measurements for an analysis cell and a voltammogram obtained by Voltammetry by potential jump from a process according to the invention for a solution of Fe ³⁺ at a concentration of 10 ^-2 mol. L ^"1 in sulfuric acid H ₂ SO ₄ at 0.5 moLL ^"1;

FIG. 4 illustrates a voltammetry obtained by voltammetry by potential jump from a method according to the invention for a solution of

Fe ³⁺ at a concentration of 10 ^{~ 3} moLL ^"1 in sulfuric acid H ₂ SO ₄ at 0.5 HiOLI / ¹ ;

FIGS. 5A and 5B respectively show the current measurements obtained for an analysis cell and a voltammogram obtained from a process according to the invention by differential pulse voltammetry for a Fe ³⁺ solution at a concentration of 10 ^{". 3} mMll ^-1 in sulfuric acid H ₂ SO ₄ at 0.5 mol. L ^"1 ;

FIGS. 6A, 6B and 6C respectively illustrate the voltammograms obtained for a Cu ²⁺ solution on a gold and copper electrode, a Cu ²⁺ solution and an Fe ³⁺ solution on an electrode. of gold, and a solution of Cu ²⁺ and Fe ³⁺ on a copper electrode.

The invention thus has a new technique for analyzing a sample of a solution by voltammetry, ensuring the renewal of the sample on the surface of the working electrode so that it corresponds to the initial composition, and which also ensures the renewal of the surface of the working electrode during the measurements necessary for the establishment of a voltammogram. According to the invention, the method uses a support having a plurality of working electrodes each belonging to a separate electrochemical analysis cell in contact with the sample, each of the working electrodes being used only for the realization of a single measurement of the sample.

An electrochemical analysis cell for the realization is composed of a working electrode, a reference electrode and a counter-electrode. The invention thus makes it possible to carry out a rigorous and rapid analysis of the chemical species present in a solution. FIG. 1 represents a voltammogram I = f (E) obtained according to a technique known from the prior art by linear potential scanning voltammetry on a gold rotating electrode forming a disk 3 mm in diameter. A saturated calomel electrode was used as the reference electrode.

The solution analyzed is a solution of Fe ³⁺ at a concentration of 10 ^-2 moLL ^"1 in sulfuric acid H ₂ SO ₄ at 0.5 rnoLL ^{" 1} . The applied potentials evolve automatically in a step of 1 mV and a speed of variation of the potential equal to 20 mV / s. This voltammogram allows to obtain the following values for the limi _you and the half-wave potential Ey _2: Iumite = 0.21 mA and Ey ₂ = 0.06 V. The Iiimi _you corresponds to the difference of the intensity between the lower and upper levels of the curve, and the half wave potential Ey ₂ corresponds to the value of the potential at the point of inflection of the curve. This value of the half-wave potential of 0.06 V is characteristic of the Fe ²⁺ ZFe ³⁺ couple under such analysis conditions (solvent: H ₂ SO ₄ at 0.5 mol -1 ^" , gold working electrode saturated calomel reference electrode).

FIG. 2A is a schematic, deliberately schematic and simplified view of an analysis support 10 according to the invention, presenting twenty distinct zones 11 each comprising a working electrode, divided into four lines of five and distant from one another .

The number of working electrodes distributed on an analysis support 10 can of course vary according to the degree of accuracy of the voltammograms that one wishes to establish. The dimensions of a working electrode can be variable.

However, the dimensions of the working electrodes of the same support, or at least the working electrodes belonging to analysis cells allowing the establishment of a same voltammogram, will be of the same shapes and dimensions. The dimensions of the surface of the working electrode affect the values of the currents during the measurements.

The distance between the different electrodes, and especially between different working electrodes, may also be variable, taking care however to avoid short circuits. The risk of short circuit is in fact a limit to the increase of the surface density of the working electrodes on the analysis support. In the case where all the electrodes (working electrode, counter-electrode and reference electrode) of an analysis cell are present on the analysis support, it is the density of these different electrodes that will be limiting.

FIG. 2B represents a zone 11 of the analysis support 10 shown in FIG. 2A. This has a working electrode 12 and a counter electrode 13 of the same analysis cell. According to this embodiment, the counter-electrode 13 surrounds the working electrode 12, made of gold for example. The analysis support 10 thus carries the working electrode 12 and the counter-electrode 13 of each analysis cell.

FIG. 2C illustrates a cross section of the zone 11 of the analysis support 10 according to FIG. 2B. Like reference numerals designate identical elements in FIGS. 2A to 2C.

The width 14 of the zone 11 comprising the working electrode 12 and the counter-electrode 13 may for example be 740 μm, the diameter of the working electrode 500 μm, and the distance separating the working electrode 12 and the counter-electrode 13 of about 30 microns.

The zones 11 comprising electrodes of different analysis cells can be separated by approximately 500 μm.

It is understood that a great modularity is possible as to the shape, the distribution, and when to the nature of the different electrodes. The analysis support 10 may be produced according to conventional techniques relating to microelectronics (for example vacuum metallization). This may for example be made of a plastic material, a resin or silicon.

In the case where the potentials are successively applied to the different working electrodes so that the measurements are carried out successively, the presence of a single electrode can be predicted. common reference to the different cells of analysis. According to the embodiment described, a saturated calomel electrode has been used, and is placed directly in the sample of the solution to be analyzed, facing the working electrodes. Moreover, the counter-electrodes 13 of the different cells can be connected together. This simplifies the manufacturing process of the analysis support by reducing the number of necessary connections.

As indicated above, it may also be provided that the reference electrode or electrodes are located on a complementary support placed facing the analysis support. FIGS. 3A and 3B respectively represent, for an imposed potential (for FIG. 3A, Ejm _P = + 0.4V) the current response as a function of time obtained for an analysis cell, and the voltammogram obtained after carrying values of the current obtained for the different cells at a constant time "t" from a twenty-cell analysis support as shown in FIGS. 2A to 2C.

The solution analyzed is, as in the previous case illustrated by FIG. 1, a solution of Fe ³⁺ at a concentration of 10 ^-2 mol ^-1 in sulfuric acid H ₂ SO ₄ at 0.5 mol -1 ^"1 .

The method used is voltammetry by potential jump on a gold electrode with a saturated calomel electrode as the reference electrode.

On the working electrode of a first cell, a base potential E ₁ of 550 mV is applied and after a time I ₁ = 100 ms, the potential is increased to E2 = 500 mV for t2 = 500 ms. The current response is read at time t ₃ = 150 ms. On the working electrode of a second cell, the starting potential E ₁ remains the same (550 mV), but the potential after 100 ms is brought to E2 = 450 mV for t2 = 500 ms. Again, the intensity of the current is recorded at t ₃ = 150 ms. The other points are obtained in the same way by lowering each time the potential E2 of 50 mV. Figure 3A shows the current response obtained for a given analysis cell as a function of time.

FIG. 3B illustrates the voltammogram obtained after carrying values of the current obtained for the twenty different cells at a constant "t" time from a twenty-cell analysis support as shown in FIGS. 2A-2C. The points represented by a square correspond to the measurements obtained for the solution containing the iron, and the curve whose points are represented by circles corresponds to the "white", that is to say to the measurements obtained for the same solution containing no iron.

A curve similar to that obtained according to the known technique of the prior art is obtained from a gold rotary electrode as represented by FIG. 1. The following values were obtained for the Iumite and for the potential of Half wave Ey ₂ : Iumite = 23 μA and Ey ₂ = 0.06 V.

Thus, as in the previous case illustrating a technique of the prior art, a value of 0.06V for the half-wave potential Ey ₂ , characteristic of the Fe ²⁺ ZFe ³⁺ pair under these analysis conditions, is obtained.

Figure 4 shows a voltammogram obtained according to the process of the invention under the same experimental conditions as above, with a ten times less concentrated solution to Fe ^3+, that is to say Fe ³⁺ at 10 ^"3 ^{moll" 1} in sulfuric H ₂ SO ₄ to 0.5 acid moll ^"1. a value for the Iumi _you 2.1 uA was obtained from this curve.

The Iumi _you depends on the concentration of the chemical species. In the present case, it is thus observed that the decrease in the concentration of Fe ³⁺ by a factor of ten with respect to the previous voltamogram represented by FIG.

3B, is substantially a decrease in the value of the

It is obtained by a factor of ten as well.

There is always a residual current corresponding to the sum of a capacitive current and to the reactions inherent to the solvent (for example decomposition of water into hydrogen in the region of the cathode potentials). It is therefore interesting to subtract this residual current from the experimental current.

It is also possible to carry out the analysis of this Fe ³⁺ solution at 10 ^-3 mol ^-1 in sulfuric acid H ₂ SO ₄ at 0.5 mol × ^-1 with a better sensitivity by the process according to the invention. using the method directly differential pulse voltammetric.

A starting potential is imposed on a working electrode of a 400 mV analysis cell for 6 s, followed by a pulse (ΔE) of 50 mV for 1 s. For the measurements by the other analysis cells, the starting potential imposed on the different working electrodes is gradually decreased by 20 mV for each of the analysis cells.

The current response over time of an analysis cell is illustrated in FIG. 5A.

The difference in current responses at constant times t ₁ and t ₂ respectively before and after the pulse gives the desired current value and makes it possible to establish the curve illustrated in FIG. 5B. The values recorded correspond to the values of the current at time ti = 5,995 s and t ₂ = 6,995 s.

The method according to the invention thus allows the analysis of chemical species of a liquid solution or a gas making it possible to quickly obtain one or more voltammograms of a sample.

In fact, the independent potentials can be applied simultaneously to the different cells and the measurements can therefore all be made simultaneously. The voltammogram (s) can be established very quickly. In addition, performing a single measurement for each analysis cell ensures the renewal of the working electrode and the sample at each measurement.

Moreover, it is possible to establish several voltammograms from the same analysis medium by combining different voltammetric methods, for example by applying different potential variations to certain sets of cells of the support.

On the other hand, it is possible to provide that the working electrodes of the different cells are of different natures. Thus, the same support may allow the analysis of species of oxidation-reduction potentials very different.

Thus in a solution of H ₂ SO ₄ for example, a working electrode in copper may allow the analysis of compounds whose oxidation-reduction potential is within a range of -0.8 to 0 V, and a gold working electrode is suitable for analysis in a range of -0, 4 to 0.8 V.

The reactivity of the species is related to the interaction they have with the surface of the working electrode (more or less strong adsorption, metallic or covalent bonding, etc ...) - Therefore, the reactivity of the different chemical species is variable depending on the nature of the working electrode.

Figures 6A, 6B and 6C are intended to illustrate this point. FIG. 6A represents the voltammograms obtained for a solution of Cu ²⁺ at 10 ^-3 mol. L ¹ by voltammetry by potential jump on a copper electrode and a gold electrode, with a saturated calomel electrode as the reference electrode.

The two curves obtained show that the copper response is much larger on the copper electrode than on the gold electrode and also shows that the reduction potentials of copper depend on the nature of the working electrode used. .

FIG. 6B shows the voltammograms obtained for a solution of Cu ²⁺ at 10 ^-3 mol- ¹ and a Fe ³⁺ solution at 10 ^-3 mol- ¹ by voltammetry by potential jump on a gold electrode, with a saturated calomel electrode as the reference electrode.

The two curves obtained show that the iron response on the gold electrode is much more intense than that of copper. On the other hand, the initial reduction potential of iron is about 500 mV while that of copper is about 35OmV.

FIG. 6C shows the voltammograms obtained for a solution of Cu ²⁺ at 10 ^-2 moLL ^"1 and a solution of Fe ³⁺ at 10 ^{" 2} mol × ^"1 by voltammetry by potential jump on a copper electrode, with an electrode saturated calomel as the reference electrode. The two curves obtained show that the iron response on the copper electrode is comparable to that of copper. On the other hand, the potential The initial reduction of iron is about -50 mV while that of copper is about -300 mV.

These curves thus show that indeed the reactivity of the chemical species is variable depending on the nature of the electrode. The fact of making and using a support having analysis cells with working electrodes of different nature makes it possible to obtain several voltammograms and to analyze a larger number of chemical species during the same analysis.

In addition, the comparison of the different voltammograms obtained allows a better determination and analysis of the voltammograms and species present. In the case presented above, we see that if the reactivity of copper and iron is similar on a copper electrode, it is not the case on a gold electrode. Thus, if a voltammogram is simultaneously established with a gold electrode for example, it will be easy to determine whether the first voltammogram obtained characterized the copper or iron present in the sample.

The technique according to the invention thus allows the realization of rigorous measurements with renewal of the electrode and the sample at each measurement and also offers a great modularity. Indeed, it will be possible to refine the analyzes by increasing the number of cells used to establish a voltammogram, to simultaneously study several potential domains, to apply several methods of voltametric analysis simultaneously, and to vary the nature of the electrodes working cells of the same analysis support.

Claims

1. Method of electrochemical analysis by voltammetry of a liquid solution, allowing detection and / or dosage in said solution of at least one chemical species, characterized in that it comprises the steps of:

contacting a sample of said solution with a single analysis support (10) having at least two working electrodes (12) each belonging to a separate electrochemical analysis cell, each analysis cell further comprising a counter - electrode (13) and a reference electrode;

performing a single and different measurement of said sample in each of said analysis cells, by applying an independent potential to each of said working electrodes (12); - establish at least one voltammogram of said sample, from said measurements;

2. Electrochemical analysis method according to claim 1, characterized in that it consists in bringing into contact a single sample with all of said analysis cells during the realization of said measurements.

3. Electrochemical analysis method according to any one of claims 1 and 2, characterized in that said measurements are performed simultaneously by said analysis cells.

4. Electrochemical analysis method according to any one of claims 1 and 2, characterized in that said measurements are carried out successively by said analysis cells.

5. An electrochemical analysis method according to claim 4, characterized in that a counter-electrode (13) and / or a reference electrode are common to at least two of said analysis cells.

6. electrochemical analysis method according to any one of claims 1 to 5, characterized in that said measurements implemented allow the implementation of at least one voltammetric analysis belonging to the group comprising: - voltammetry jump potential;

- normal impulse voltammetry;

differential pulse voltammetry.

7. Device for implementing an electrochemical analysis method according to any one of claims 1 to 6, characterized in that it comprises means for applying an independent potential to each of said working electrodes. (12) and measuring said sample in each of said analysis cells.

8. Device according to claim 7, characterized in that it comprises third means for receiving a complementary support according to claim 15, and in that it comprises means for contacting said sample and said complementary support.

9. Device according to any one of claims 7 and 8 characterized in that it comprises means for establishing at least one voltammogram from said measurements.

10. Device according to any one of claims 7 to 9, characterized in that it comprises means for deducing said at least one voltammogram information relating to the detection and / or dosage of said at least one chemical species in said sample.

11. Device according to any one of claims 7 to 10, characterized in that it is portable.